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 TM 11-5895-1847-12&P
0003 00
DESCRIPTION OF THE GMDSS NAVIGATION POWER SUPPLY
The GMDSS navigation power supply (21), located above the chart table, powers the NAVTEX receiver and the
navigation PLGR (through the navigation interface and switchbox). The navigation power supply receives 115 vac
power from the ship's alternating current power circuit and converts the power to 13.6 vdc.
DESCRIPTION OF THE DSC VHF/FM TRANSCEIVER
The DSC VHF/FM transceiver (22) is an all channel Digital Selective Calling (DSC) Frequency Modulation (FM)
transceiver operating in the Very High Frequency (VHF) marine frequency range. The transceiver employs the latest
frequency and microcomputer technology to provide a high performance, reliable communication system for both
military and commercial mariners. The DSC features make the transceiver the most advanced marine VHF
communication system available. Also, a two-way data communications interface allows automatic position
reporting. The transceiver system consists of the compact transceiver with microphone, accessories and cables for
installation and electrical connection. The transceiver enables the operator to program into the radio DSC numbers
for other vessels, marinas, bridge tenders and coast stations. DSC ship station identification numbers are issued by the
FCC or DOC (Canada) and appropriate communications authorities in other countries.
DSC Calling
The DSC offers many Digital Selective Calling features to improve communication effectiveness and reduce channel
congestion. The Digital Selective Call functions of the DSC are divided into four different operating modes: the DSC
mode is for placing individual and group calls, the ANSWER mode is for returning received calls. The TELephone
mode is for placing phone calls and the SCRambler mode is used to keep conversation private. Each mode has one or
more directories and other supporting functions to enhance the DSC communication capability.
All DSC calls are automatically sent and received on channel 70. Channel 70 has been designated specifically for
DSC service and must not be used for voice communication. The DSC calling procedure requires the selection of a
working channel prior to making a call. After DSC contact is established on channel 70, the transceiver automatically
switches to the selected working channel for routine communication.
In order to use the DSC mode to send and receive calls, two things must be done. Your ship station identity number
must be entered into the USER DSC ID page of the USER SETUPS mode. Please see USER SETUPS for the
procedures (WP003300). The name and ship station Identity number of at least one other DSC equipped vessel must
be entered into the DSC calling directory.
Most of the DSC functions of the DSC are accessed through the DSC mode. The SCRambler, TELephone, and
ANSwer modes are all DSC functions as well but since they are more specific in their purpose they are treated as
individual modes. The general arrangement of the menus and data pages is the same for all DSC modes.
Directories
The DIRECTORY is the data base for placing and answering DSC calls. Both vessel names and ship station identity
numbers are entered into the directories. Although only the Ship Station Identity numbers are used to place and
answer calls, having the corresponding names make selection and identification much easier.
There are five directories used for either sending or receiving DSC calls. They are: DSC CALLING for calls to other
vessels and to private coast stations, GROUP CALLING for ship to ship group calls, TELEPHONE and COAST
STATION directories for placing unattended calls to residence or business telephones and CALL WAITING for
logging and returning received DSC calls. Another directory, DISTRESS DATA, logs vessel ID, time, and position
of vessels sending DSC distress calls.
The DSC CALLING directory's purpose is to store the user's list of vessels or coast stations and their ID number for
use in placing DSC calls. When a DSC call is made, the vessel's name or ID number is first selected from
the directory.
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